#include <study.hpp>
 
// Lesson:  Find average of several doubles
// Every exercise will consist of a number of non-negative doubles, followed
// by a -1.0.  Once this is read, the average of the doubles should be printed
// (the -1.0 should not be included in the count).
 
// Syntax: Check stream state for end of lesson, check values for end of exercise.
int main()
{
	while(study::cin) // Will be false after the last exercise
	{
		double d;
		double total = 0.0;
		int count = 0;
		while (study::cin >> d && d != -1.0) // study::cin >> d will always be true.
		{
			total += d;
			++count;
		}
		study::cout << (total/count) << study::endl; // Submits the answer.
	}
}
 

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